1. Field of the Invention
This invention relates to semiconductor devices, Micro Electro Mechanical Systems (MEMS), sensors and more specifically to three dimensional (3D) three-axis finger force sensors, finger-mouse and micro-joysticks for consumer and other applications.
2. Background
The 3D force sensors based on micromachined silicon chips with piezoresistors on the flexible diaphragm are known. Prior art shown in FIG. 1, uses a sensor chip 10 from a rigid frame 12 and rigid central part 16 of a die, boss, connected with the frame by a thinner diaphragm 14. The piezoresistors 18,24 are located at the periphery of the diaphragm adjacent to the frame 12 and to piezoresistors 20, 22 are adjacent to the boss 16 and electrically connected into three Wheatstone bridges through contact pads 26,28,30,32 accommodating X, Y and Z components of an applied force vector. The disadvantages of these kinds of known solutions can be summarized as: poor long-term stability due to the metal on the suspension; limited mechanical overload protection; large difference in X, Y, Z sensitivities; large cross-axis sensitivity; no process integration with other sensors and CMOS; no scaling; no solutions for convenient application from an external force; no solutions for providing required combination of applied force and deflection. Furthermore although there is a market need, no such semiconductor components reached the consumer market due to their high cost.
However there is a need for 3-dimensional input force control devices, which would be low cost, small, reliable, stable, providing required ratio between X,Y,Z sensitivities, low cross axis sensitivity, process integration with other sensors and CMOS, further scaling, convenient solutions for applying an external force, required combination of applied force and deflection and manufacturability for high volume consumer markets like cell phones, portable gamers, digital cameras, etc, using user tactile force inputs as part of the user interface. Furthermore, the need for 3-dimensional input control extends beyond X, Y, Z rectilinear coordinate system to any orthogonal system position translation mappings or non-position dimensionality component mappings as well.